The present invention relates to the purification of plutonium which is separated from fission products and from uranium during the reprocessing of irradiated nuclear fuel.
In one process for the reprocessing of irradiated nuclear fuel the nuclear fuel material and fission products are dissolved in nitric acid and the resulting solution is passed to a solvent extraction column where it is brought into contact with a solution of tributyl phosphate in kerosene. The extractable species which include plutonium, uranium and neptunium values pass into the organic phase leaving the bulk of the highly radioactive fission products in the aqueous phase. The organic phase is then passed to a further solvent extraction column where it is brought into contact with an aqueous solution of a reducing agent such as tetravalent uranium which is capable of reducing tetravalent plutonium to the trivalent state. Trivalent plutonium passes into the aqueous phase along with some uranium and neptunium and other impurities. The uranium present is not reduced by the reducing agent and the major proportion of it remains in the organic phase. Following this primary separation of the uranium-containing organic phase and the plutonium-containing aqueous phase, further purification is required to isolate the uranium and plutonium in a suitable form for re-using as fuel for a nuclear reactor. It is the further purification of the plutonium-containing aqueous phase to which the present invention relates.